Many communication systems require a low profile aperture antenna that can be easily conformed to an existing structure, such as the skin of an aircraft, or concealed beneath a surface, that can be used on a moving vehicle, and that can provide a steered beam. In the past, monolithic microwave integrated circuit (MMIC) or other electronically scanned or steered planar phased arrays have been used for such applications because they provide a low profile aperture. The usual reasons why an electronic phased array may be selected for a particular application include the phased array's ability to provide high speed beam scanning and meet multi-beam/multi-function requirements.
Unfortunately, there are several disadvantages associated with implementing an electronically steered phased array. The most notable disadvantage is that electronically steered phased arrays are very costly, since the amplitude and phase at each point in the aperture is controlled discretely. The active circuit elements required to operate such an array are complex, costly and susceptible to failure. As a result, commercial exploitation of electronically steered phased arrays has been limited. Instead, the use of electronically steered phased arrays is generally confined to applications where minimizing cost is not necessarily of the highest priority. However, for most commercial applications mitigating costs is a high priority when implementing antennas or other devices.
An alternative to electronically steered phased array antennas is a mechanically steered antenna. Mechanically steered antennas include directional antennas, such as dishes, that are mechanically moved so that they point towards the endpoint that they are exchanging communications with. Other examples of mechanically steered antennas include antennas with beams that can be steered by rotating one or more lenses that intersect the antenna's beam. However, directional antennas that are mechanically steered often have a relatively high profile, and are therefore unsuitable for applications requiring a low-profile antenna. An antenna with a mechanically steered lens assembly can suffer from increased losses due to the inclusion of the lens elements and, like other systems that include mechanically steered components, can be prone to mechanical failure.
Still another alternative is to substitute an antenna with a higher gain omnidirectional azimuth plane pattern for an antenna with a beam that can be steered. However, many antenna designs that produce a suitable omnidirectional azimuth plane pattern have a relatively high profile and reduced coverage in the elevation plane. In addition, the gain of such systems for a particular antenna size or configuration can be inadequate for certain applications. Moreover, for particular applications, it may be undesirable to utilize an omnidirectional beam pattern.